Speed vs. RPM

jddens · Post by **jddens** » Wed Feb 08, 2012 6:36 pm

This topic has come up on another thread but didn't want to hijack it so I'm going to start a new one.....

What types of speed are people getting and at what RPM. After reading the other thread I got to thinking maybe I should have more speed and lower RPM than I do.....twin 350's, 330hp(way more than the original 302's) running through Hurth ZF direct drives.

At 18-20 knot cruise (GPS) I'm turning about 3200rpm....next time I'm out I'll take some additional notes of RPM's at other speeds, both up and down the road.........Are these number similar to what other are getting?

I'm not sure of the ratio of the trans the props are 15X17.............John

alexander38 · Post by **alexander38** » Wed Feb 08, 2012 6:40 pm

really need what your rpm should be at wot and trans ratio...then let the worms come out of the can that you've opened

captainmaniac · Post by **captainmaniac** » Wed Feb 08, 2012 6:41 pm

Summarized from my records; average speeds over the past 12 years at different rpms... F32 with twin Chrysler 360s.

rpm Total
1000 5.00
1500 8.00
2100 9.50
2500 14.00
2800 17.00
3000 19.00
3200 21.00
3400 23.00
3500 24.00
4000 27.00

Stripermann2 · Post by **Stripermann2** » Wed Feb 08, 2012 6:43 pm

John,
I'm turning close to the same...19-21 kts. at about 3100 rpm. Of course a few factors will give or take those numbers.
350 Chevys (small block) 16X16 props, clean bottom. Moderate boat load.

k9th · Post by **k9th** » Wed Feb 08, 2012 6:59 pm

My owner's manual for my '79 tri-cabin lists various engine packages available along with RPM/Speed/Range charts for each engine package. When I checked it against my Merc 255s, it was right on the money. I cruise at 18kts @ 2,900 RPM in relatively smooth water with light winds.

foofer b · Post by **foofer b** » Wed Feb 08, 2012 7:20 pm

Jamie, I love your new avatar.

proudfox · Post by **proudfox** » Wed Feb 08, 2012 7:24 pm

I wondered if you would all share what you average gas consumption
is at 2500 rpm, relative smooth seas, boat full of fuel 200 gallons,
clean bottom, two people onboard, twin chrysler 360 engines, total hp
is 500.

Thank you

captainmaniac · Post by **captainmaniac** » Wed Feb 08, 2012 7:38 pm

proudfox wrote:I wondered if you would all share what you average gas consumption
is at 2500 rpm, relative smooth seas, boat full of fuel 200 gallons,
clean bottom, two people onboard, twin chrysler 360 engines, total hp
is 500.

Thank you

I don't have specific values by RPM, but in general at that speed I am around 1.0 - 1.1 mpg. In good conditions and no headwind the 1.1 is usually attainable.

Vitaliy · Post by **Vitaliy** » Wed Feb 08, 2012 9:28 pm

my 74 f36 tri with twin 454's at about 3k RPM is pushing 21 knots based on the GPS.... burns a hell of a lot of gas thou

Vitaliy · Post by **Vitaliy** » Wed Feb 08, 2012 9:29 pm

forgot to mention that on average i get .9ish to the mile so in compression to you guys its really not all that to bad, i tend to stay at the 2500 RPS mark while just cruising thou, got the engines to idle at about 600 RPM

jordan · Post by **jordan** » Wed Feb 08, 2012 9:30 pm

Captainmaniac, my numbers and fuel mileage is almost identical to yours even though I have Chrysler 318s. My max speed on gps is 26 nmph at 4000 rpm. Fuel useage seems to be 1 nmpg at just about any speed until the four barrels open, then I don't want to know what I'm getting!

captainmaniac · Post by **captainmaniac** » Wed Feb 08, 2012 9:57 pm

My 1.0 - 1.1 is actually overall. At fast idle speeds (1500 rpm -> 8 knots) I am about 1.5 mpg; but at 2800-3200 the 4bbls haven't opened yet and 1.1 is about right. I don't tend to push it beyond that. I have for short stints from time to time (no more than 5-10 mins per shot) but generally only to hit a lift bridge that only opens every half hour (lower economy for 5 mins to make the bridge vs a half hour even at idle... you decide).

I am also running with almost 1700 hrs on (at this point) 33 year old engines.

gettaway · Post by **gettaway** » Wed Feb 08, 2012 10:12 pm

twin 165's at 10 knots 6 gph total turning 16 X 14 screws

prowlersfish · Post by **prowlersfish** » Wed Feb 08, 2012 10:50 pm

Vitaliy wrote:forgot to mention that on average i get .9ish to the mile so in compression to you guys its really not all that to bad, i tend to stay at the 2500 RPS mark while just cruising thou, got the engines to idle at about 600 RPM

.9 average ? what is your averge crusine speed ? the reason I ask is you MPG is almost that of Diesels on a boat your size . Do you do A lot of low speed running ?

alexander38 · Post by **alexander38** » Thu Feb 09, 2012 3:36 am

gettaway wrote:twin 165's at 10 knots 6 gph total turning 16 X 14 screws

Smarta$$

so have you got a on plane burn rate yet ?

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Speed vs. RPM

Speed vs. RPM

Gasoline consumption at 2500 rpm- twin Chrysler 360 -32 FSB

Re: Gasoline consumption at 2500 rpm- twin Chrysler 360 -32